# fpclassify

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< c‎ | numeric‎ | math

Defined in header ``<math.h>`` |  |
#define fpclassify(arg) /* implementation defined */ |  | (since C99)

Categorizes floating-point value arg into the following categories: zero, subnormal, normal, infinite, NAN, or implementation-defined category. The macro returns an integral value.

FLT_EVAL_METHOD is ignored: even if the argument is evaluated with more range and precision than its type, it is first converted to its semantic type, and the classification is based on that: a normal long double value might become subnormal when converted to double and zero when converted to float.

### Parameters

arg | - | floating-point value

### Return value

One of FP_INFINITE, FP_NAN, FP_NORMAL, FP_SUBNORMAL, FP_ZERO or implementation-defined type, specifying the category of arg.

### Example

Run this code

    #include <float.h>
    #include <math.h>
    #include <stdio.h>

    const char* show_classification(double x)
    {
        switch(fpclassify(x))
        {
            case FP_INFINITE:  return "Inf";
            case FP_NAN:       return "NaN";
            case FP_NORMAL:    return "normal";
            case FP_SUBNORMAL: return "subnormal";
            case FP_ZERO:      return "zero";
            default:           return "unknown";
        }
    }

    int main(void)
    {
        printf("1.0/0.0 is %s\n", show_classification(1 / 0.0));
        printf("0.0/0.0 is %s\n", show_classification(0.0 / 0.0));
        printf("DBL_MIN/2 is %s\n", show_classification(DBL_MIN / 2));
        printf("-0.0 is %s\n", show_classification(-0.0));
        printf("1.0 is %s\n", show_classification(1.0));
    }

Output:

    1.0/0.0 is Inf
    0.0/0.0 is NaN
    DBL_MIN/2 is subnormal
    -0.0 is zero
    1.0 is normal

### References

- C23 standard (ISO/IEC 9899:2024):

  - 7.12.3.1 The fpclassify macro (p: TBD)

- C17 standard (ISO/IEC 9899:2018):

  - 7.12.3.1 The fpclassify macro (p: TBD)

- C11 standard (ISO/IEC 9899:2011):

  - 7.12.3.1 The fpclassify macro (p: 235)

- C99 standard (ISO/IEC 9899:1999):

  - 7.12.3.1 The fpclassify macro (p: 216)

### See also

isfinite (C99) | checks if the given number has finite value (function macro)
isinf (C99) | checks if the given number is infinite (function macro)
isnan (C99) | checks if the given number is NaN (function macro)
isnormal (C99) | checks if the given number is normal (function macro)
C++ documentation for fpclassify

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